The present invention relates to a method of backing up data, specifically to a method of mutually backing up data by use of plural information processing units connected to a network, a method of restoring backed-up data, and a system of the same.
It is a common practice to connect information processing units such as computers and storage devices to a network, and to process information while exchanging data between these units. Some storage devices for recording bulk data employ the RAID (Redundancy Arrays Of Inexpensive Disks) these days, and practically use the management technique that integrates the storage devices while using the SAN (Storage Area Network) with the NAS (Network Attached Storage). These information processing units such as computers and storage devices can write and read data, and they are often referred to as media. As long as it can write and read data, the media include an information processing unit that is not necessarily connected to a network.
A general behavior prepares the so-called backup of retaining the copies of currently used data in the other media, in order to prevent the data from disappearing, or to ensure the security of the data. When the media is connected to a network, the backup of data in general automatically stores the data in a different medium by a computer or a timer issuing a periodic trigger. When the medium is not connected to a network, on the other hand, the operator manually issues a trigger for the backup to retain the data in a different medium.
In this method, the medium being the storage unit destined for the backup data, or the backup time is settled in advance. Accordingly, in an accident or a disaster, since the medium destined for the backup or the backup time is settled, there is a fear that this method cannot make the backup of the data, and can lose the data.
As the technique to back up data in the media utilizing a network, the Japanese Published Unexamined Patent Application No. 2002-215474, for example, proposes a technique to back up data on a network to which plural servers are connected. This method creates a mirror of the data in more than two servers connected with the network, in which the plural servers monitor the situations of themselves each other. As a result of the monitoring, when detecting an abnormality in one server, the method makes the servers cooperate to find out a server having sufficient storage capacity, determines a substitutive server, and transfers the data to the substitutive server to store the data. In this manner, the above technique discloses a backup system, in which plural backup servers are always formed.
The Japanese Published Unexamined Patent Application No. 2003-223286 proposes a storage system provided with an autonomously functional storage device, whereby a management server is made unnecessary. That is, in the storage system, a copy agent possesses the duplicate function of a copying unit, a monitoring unit monitors the multiplicity of the copying unit, and when the multiplicity is insufficient, the system issues a duplicate request to other storage devices.
The technique disclosed in the Japanese Published Unexamined Patent Application No. 2002-215474 searches for a substitutive server having a margin in the storage capacity, and sends the data to the substitutive server having the margin. However, this technique requires the substitutive server to monitor the multiplicity of the copying unit in the other storage devices. The Japanese Published Unexamined Patent Application No. 2002-215474 does not disclose a concrete method how to search for the substitutive server having the margin.
The technique disclosed in the Japanese Published Unexamined Patent Application No. 2003-223286 saves the management server; however, the technique needs to autonomously monitor the other storage devices. The Japanese Published Unexamined Patent Application No. 2003-223286 does not relate how to restore the data having been backed up.